That palette carefully changes, though, in the new “Homicide: The Graphic Novel, Part One,” which becomes a mostly monochromatic noir — the scenes of Charm City’s rough corners and tough interrogation rooms often rendered in shades of gray, punctuated by the occasional eye-pop tint of an orange prisoner jumpsuit, the pale yellow of crime-scene police tape or the liquid crimson of a fresh victim’s blood.

The illustrated book from French graphic novelist Philippe Squarzoni, published this week — as adapted from the original in consultation with Simon — is as beautifully stark as the hard-boiled Hollywood adaptations of another former Baltimore Sun reporter, legendary noir author James M. Cain. And Simon approves.

“Sure, who doesn’t like noir?” Simon says with an up beat by phone last month. He’s on the Acela train en route to New York, where he plans to picket the next day outside HBO on behalf of his fellow screenwriters.

Comics aren’t necessarily his thing. He did read military comic books as a kid, and he’s a fan of “Doonesbury” and “Maus.” He’s also aware of the graphic novels by George Pelecanos, who has worked on multiple much-lauded HBO shows with Simon, including “The Wire,” “Treme” and the 2022 limited series they co-created, “We Own This City.”

Yet the “Homicide” graphic adaptation, which is scheduled to publish its second part in December, is prompting Simon to reflect on his original book, published in 1991, and on the year he spent embedded with Baltimore homicide detectives 35 years ago. So much about American police work is different since 1988: the “murder clearance” rate (how many homicides are solved and “cleared”) has dipped precipitously, for instance, and the use of forensic science has led to hundreds of exonerations by DNA since 1989.

Simon was a young crime reporter for the Sun in the mid-’80s when, at Christmastime, he dropped off a bottle of cheer for the homicide detectives. It was a fairly slow night, so he drank with them as they poured shots. As Simon recalls, a detective named Bill Lansey then said: “If somebody could get up here and just follow all the s— that happens, they would have a book.” Lansey wasn’t even looking at the reporter, but Simon recollects: “It stayed in my mind.”

Cut to a couple of years later, and Simon is “feeling a little bit mad” over labor unrest at the Sun. Hungry for a change, he writes a letter to the police commissioner, asking for permission to go into the Baltimore Police Department’s homicide unit as an observer for a year, to chronicle the lives and actions of several dozen detectives. “Incredibly,” Simon recalls, “he said yes.”

Soon, Simon is covering the grind of this life. He illuminates the joking detective who will deliver the deadpan while standing over a dead man. There’s the tough rookie who will exceed expectations. Shift commanders, squad supervisors, higher-ups: Amid the body count, detectives must survive the bureaucracy. And always, there is the big office board that lists open and cleared cases in red and black ink, respectively.

The young reporter peels back the layers of the “graceless, nocturnal ballet” at headquarters, he writes, as witnesses glide “past one another beneath the washed-out glare of tube lighting, each flanked by a tired, impassive detective cradling black coffee and enough blank statement forms to record the next round of half-truths.”

And often, Simon demystifies the work that Hollywood has long shellacked with glamour. He portrays the kind of job where you sit behind a metal desk in a poorly ventilated “steel-frame death trap,” eating cheap pizza and Italian cold cuts as “Hawaii Five-O” reruns blare in the background. After a dispatcher calls, you will grab your gun, notepad, flashlight and rubber gloves, climb into an unmarked Chevrolet Cavalier and drive to where “in all probability, a uniformed police officer will be standing over a cooling human body.” Later, you will “throw as much street-corner psychology as you can at the people who found the body.”

Yet scarred neighborhoods tend to move on from each murder. Simon calls West Baltimore the “home of the misdemeanor homicide.” And he writes that, in a city “with 240 murders a year, there will always be another body.”

Reviews called the 1991 book “one of the most engrossing police procedural mystery books” and a “masterpiece” that captures “the poetry of the meanest streets.” And in the “ante mortem” to the book, novelist and screenwriter Richard Price (“Clockers”) writes that “through the steadfastness of Simon’s presence Homicide offers us the patterns hidden within the chaos. Baltimore, in fact, is Chaos Theory incarnate.”

Flash-forward to a French comic artist visiting the United States: Squarzoni knew of Simon’s later screen work, such as “The Wire” and “Generation Kill,” when he happened to spot “Homicide” in a Portland bookstore. He cracked open the cover and had a creative epiphany.

“Reading the book — and that’s the only time it’s ever happened to me — I could see the comics pages appear in my mind,” the Lyon-based Squarzoni says via email, as translated by his American editor, Mark Siegel. “I could sense the graphic novel it wanted to be. Intuitively, I knew the look and the page compositions it would call for.” He contacted his editor and said: “This is my next book.”

Eventually, Squarzoni managed to get a letter into Simon’s hands to explain his vision. “He gave his blessing, with the only condition being that I faithfully follow the chronology and the facts as they unfolded in that year, 1988,” the artist writes.

Simon and Squarzoni communicated virtually during the graphic novel’s creation. (They’ve never met in person.) “He had more questions from a visual nature of things: ‘What kind of handguns do they carry? Where do they wear the holsters?’” Simon says.

The multivolume adaptation was first published in France. Simon sent French-language editions to dozens of surviving detectives. He thought they’d get a kick out of it, although “I don’t think most of them parlez-vous,” Simon says with a laugh.

First Second Books, the graphic novel imprint of Macmillan, leaped at the opportunity to publish this year’s two-book English translation.

Simon underscores that the graphic novel’s timing is potently different: “Philippe is bringing this book out in that moment in America where people want to doubt the very fundamentals” of police work, he says.

Still, Simon believes that, “at the end of the day, you want it to be that when someone goes and shoots somebody and takes a life,” that law enforcement “follows up and tries to arrest them and hold them to account for taking a human life.”

“It’s sort of a basic premise that survives even in our current moment of, ‘All cops are bastards,’ and ‘defund’ and whatever else is the slogan of the moment.”